The observation of quantum transport phenomena in metals and semiconductors is limited by the eventual loss of phase coherence of the conducting electrons on the time scale τ_φ (dephasing time). We addressed the question whether τ_φ saturates at low temperatures. We used weak localization (WL) studies to measure τ_φ in a two-dimensional electron gas (2DEG), in GaAs/AlGaAs heterostructures at low temperatures. We used a novel temperature calibration method based on the Integer Quantum Hall Effect, in order to ascertain the temperature of the 2DEG when there is a lack of good thermal contact with the bath. We claim that the apparent saturation is an outcome of electron heating due to electromagnetic radiation or some other extrinsic source, and that therefore, it does not represent any dephasing-time saturation as such.